Metamorfismo da sequência Anicuns-Itaberaí na região de Nazário-GO

Abstract

The Anicuns-Itaberaí Sequence is one of the metavolcanosedimentary sequences that make up the Arenópolis Magmatic Arc. However, even with the abundance of research found in the literature related to geochemical, isotopic and geochronological aspects, there is still little material on petrology and structural geology with a focus on the metamorphic evolution of these rocks, which makes the tectono-metamorphic evolution of these sequences still poorly understood. This work aimed to establish, through geological mapping, structural interpretation and petrological studies, a greater understanding of the metamorphic conditions (P-T) that the rocks of the Anicuns-Itaberaí Sequence were subjected to during the metamorphic evolution of the Brasília belt. The results of this work include geological mapping on a scale of 1:50,000 of the region bordering the municipalities of Anicuns, Avelinópolis, Nazário and Palmeiras de Goiás. It also includes the integration of structural, microstructural and petrological data, and the creation of compositional maps of two samples of garnet-chlorite-biotite-muscovite schist from the area that were made using XMapTools software from electron microprobe data. The mineral assemblage of these rocks, given by garnet + plagioclase + biotite + muscovite + quartz + chlorite, was modeled geothermobarometrically using the Bingo-Antidote extension. The modeling results suggest that the metamorphic peak occurred in amphibolite facies conditions (staurolite zone), with retrometamorphism during crustal exhumation to green schist facies conditions. The results show small differences in values between the samples. In sample 23GO_022-P1 the conditions obtained were 630.9 °C and 1.007 GPa for the peak of metamorphism and 536.6 °C and 0.588 GPa for retrometamorphism, while for sample 23GO_025-T1 the conditions were 654.2 °C and 1.198 GPa for the metamorphic peak and 569.9 °C and 0.703 GPa for retrometamorphism. These values indicate that, although there is a small difference between the P-T results between the two samples, the P-T amplitude between the metamorphic peak and the retrometamorphism are very similar for the two samples, which suggests that these differences may be related to different levels of burial between the two samples during the metamorphic process. Finally, it should be emphasized that the data presented in this work provides new information on the geological evolution of these rocks and also shows the need for more studies of this type in the area, including geochronological data on metamorphic rocks in order to better understand the relationship between metamorphism and the tectonic events that affected the region.